The Migration Observatory’s analysis, by Dr Alessio Cangiano, shows that more than half (51%) of the increase in the UK’s population between 1991 – 2014 was due to the direct contribution of rising net migration. Overall during this period net migration contributed an additional 3.8 million people to the UK. Immigration also makes an indirect contribution to population change, mainly through births as migrants are predominantly young, healthy individuals. A recent ONS report (Dorman, 2014)* using the latest census data for England and Wales, showed that births to foreign-born women made up 25.5% of all births in 2011, up from 16.4% in 2001. This was largely due to an increase in the number of women of child-bearing age, rather than from foreign-born women having a higher fertility rate than UK-born.

Setting out a range of scenarios, varying between low migration projections to high migration projections to 2039, the Migration Observatory’s briefing suggests that on average the population of the UK is set to increase by nearly 10 million people over the coming decade, reaching 70 million by 2027. Under the low migration scenario, which estimates net migration at 105,000 per annum over the long term, the population would reach 71.8 million people by 2039. A high migration scenario, with a long-term trend of 265,000 people per annum entering the UK, would see the population rise to 76.8 million over the same time scale. Dr Cangiano compared these projections to a ‘zero net migration’ projection, in which future population change is driven only by natural change (equal levels of emigration and immigration, with change driven by births and deaths). Comparisons of the zero net migration projection to the ‘principal projection’, seen as the most likely of the modelled scenarios, in which net migration is assumed to level off at 185,000 per year after 2020-21, illustrates that the cumulative net inflow of post-2014 migrants will account for 51% of total population growth by 2039.

Yet projecting changes in population over time are notoriously difficult. The Migration Observatory’s analysis acknowledges that future international migration is particularly hard to model as migration flows are often affected by sudden changes in economic, social and political circumstances which are both hard to predict and hard to quantify. Past projections for UK population change which took 1994 data as a baseline, for example, suggested that net migration in the UK would return to zero in the long-term. The balance between emigration and immigration to the UK that was observed in the 1980s and early 1990s was taken as a reference point, indicating that the population of the UK would peak at 61 million in 2023 and decline thereafter. Since then, projections have had to be revised upwards to account for rapid increases in migrant flows, along with some improvements in modelling techniques.

And what of current migration levels? The figures from the ONS released last week show that annual net migration in the UK to the year-ending September 2015, increased by 31,000, to 323,000, although this increase was not statistically significant, compared to the year-ending September 2014. The increase was due to a decline in emigration from the UK (again not statistically significant), rather than an increase in immigration levels, which remained broadly similar to the previous year. Madeleine Sumption, Director of the Migration Observatory, on commenting to the Guardian about the statistical release suggested that policy-makers should question whether “we are experiencing a temporary peak or a ‘new normal’ in the UK”. She continued: “In the short term, the UK remains an attractive destination with low unemployment and robust job growth so there’s no reason to expect a dramatic change to migration levels. In the long run, migration is much harder to predict. It will depend on many different factors from future policy changes to economic growth in other countries.”

The UK’s Government’s current attitude to high net migration was encapsulated by a quote in the same article from the Home Secretary, Theresa May: “Net migration in the UK still remains too high. Immigration at this level puts pressure on public services, on housing, on infrastructure … it can hold down wages and push British workers out of jobs.”